Prosthetic heart valve with increased valve lumen

ABSTRACT

A heart valve prosthesis having a valve housing providing a lumen therethrough. The valve housing has a first annulus on one end and a second annulus on the other end spaced apart from the first annulus. A suture cuff is used for attaching the valve housing to heart tissue of a patient. The cuff is attached between the first annulus and the second annulus. The cuff is positioned such that prosthesis is attached in a supra-annular position relative to a tissue annulus of the heart. The design allows for an increased valve lumen.

FIELD OF THE INVENTION

This is a Continuation-In-Part application of U.S. Ser. No. 08/476,223,filed on Jun. 7, 1995, now abandoned.

The present invention relates to prosthetic heart valves. Moreparticularly, the invention relates to an increased valve lumen of aprosthetic heart valve to improve hemodynamic performance.

BACKGROUND OF THE INVENTION

Prosthetic heart valves are used as a replacement for natural heartvalves of patients. A standard implantable mechanical heart valvetypically includes an annular valve housing or body (often called an“orifice”) to provide a lumen or passageway therethrough for blood flow.One or more occluders mounted to the valve are movable between an openposition, allowing blood flow, and a closed position which blocks bloodflow. In many mechanical valves, the occluders are essentiallyplate-like members called “leaflets.” Typical configurations includeone, two or three leaflets in the valve body.

An attachment mechanism typically surrounds the valve body and is usedto secure, typically with sutures, the valve to the patient's hearttissue. While some early prosthetic valves used hooks or barbs forattachment, a fabric suture or sewing cuff which is secured to theannular valve housing is typically used. Attachment of the suture cuffto the valve may be through any of a number of different retentiontechniques, some of which provide rotatable coupling. For example, U.S.Pat. No. 5,360,014 shows a separate stiffening ring which carries asuture cuff and which is clipped to the valve body by a lock wirebetween the valve body and the stiffening ring.

There has been an ongoing effort to improve the efficiency of prostheticheart valves. One critical factor in heart valve efficiency is the totalarea of the lumen when the leaflets are in an open position. Forpatients with small aortic roots (typically defined as a tissue annulusdiameter of between about 17 mm and about 21 mm), there have beenindications that available prosthetic valves are stenotic when comparedto the healthy native valve. The orifice or lumen area of typicalprosthetic valves is so small that the left ventricle may be undulyburdened in maintaining an adequate cardiac output. The effectiveorifice area is further reduced by the hydrodynamic impedance of thevalve. It has been found that currently available small prostheticaortic valves are associated with decreased tolerance to exercise,reduced rate of regression of left ventricular hypertrophy and a higherincidence rate of congestive heart failure. (See “Prosthetic Valves forthe Small Aortic Root,” Journal of Cardiac Surgery, 1994; 9 [suppl]:154-157, by H. B. Barner, A. J. Labovitz and A. C. Fiore.)

One technique which provides a less stenotic replacement valve involvesenlargement of the aortic root and tissue annulus by the surgeon.However, such procedures introduce additional risk to the patientbecause they require greater manipulation and excision of tissue.Further, these procedures require an increased duration of heart-lungbypass, thereby imposing additional risks to the patient from thatprocedure. Another surgical approach for implanting a less stenoticvalve has been to implant tissue valves such as allografts and stentlessheterografts in these patients. However, for many patients, thewell-established durability of mechanical heart valves is preferred.

To meet the need for less stenotic small prosthetic heart valves,changes in mechanical valve sewing cuff configurations have beenintroduced. This has allowed implantation of valves having a lumendiameter typically one size (2 mm) larger than has been previouslypossible. For example, the tissue annulus of the standard mechanicalheart valve from St. Jude Medical, Inc., of St. Paul, Minn., lies onsewing cuff fabric which extends from a pyrolytic carbon orifice ring.In the Hemodynamic Plus (HP) Series mechanical heart valve alsoavailable from St. Jude Medical, Inc., the sewing cuff lies entirelybetween cuff retaining rims of the orifice ring so that the cuff isimplanted supra-annularly and the upstream retaining rim periphery orcircumference constitutes the valve surface (the “valve tissue annulus”)engaging or apposing the heart's tissue annulus which remains afterexcision of the native valve. The intra-annular and subannularprojection of this valve reduces the potential for tissue overgrowth ofthe valving mechanism and maintains the patency of the valve and tissuelumens.

Another prior art prosthetic heart valve is depicted in U.S. Pat. No.5,360,041, issued Nov. 1, 1994. In this configuration, the valve iscompletely supra-annular. The suture cuff forms a brim which surroundsthe extreme edge of the upstream annulus of the orifice ring. Althoughthis may allow for increased valve and lumen size, the highsupra-annular profile of the valve has, in at least some patients,blocked the right coronary ostium. Further, the position of the suturecuff may render the valving mechanism relatively vulnerable to tissueovergrowth. In addition, there is no intra-annular barrier to retardgrowth of tissue into the valve lumen.

While recent developments in prosthetic heart valves, such as thosedescribed above, have provided improvements, they remain stenoticcompared to the healthy native valve. Improvements to further decreasethe transvalvular pressure gradients of forward blood flow would bebeneficial to patients. Although small, non-stenotic replacement valvesare typically needed for the aortic position, there is also a need forsuch valves for the mitral position, typically in pediatric cases.

Another problem which may be associated with replacement heart valveswith small lumens relates to formation of thrombus and thromboembolism.Thrombus and thromboembolism are known complications of mechanical heartvalves and can result in serious disability or death. To help preventthese complications, a common treatment involves life-long anticoagulanttherapy. However, anticoagulant therapy itself leads to an increasedrisk of anticoagulant-related hemorrhage.

Factors which influence the risk of thrombus and thromboembolismformation for mechanical heart valve patients include thenonphysiological surfaces and blood flow introduced by mechanicalvalves. Further, typical mechanical heart valves subject the blood tohigh shear stress, largely because the relatively small lumens of suchvalves tend to produce high velocity forward flow as the heart strivesto maintain adequate cardiac output. Since the blood flow velocityimmediately adjacent to the walls of the valve lumen and the occludersmust be zero, large velocity gradients are generated during forward flowas a consequence of the high mean velocity. The shear stresses areproportional to the velocity gradients. High shear stresses are known toactivate blood platelets and damage red blood cells. Such damaged redblood cells release a biochemical agent, adenosine 5′-diphosphate (ADP),which further activates platelets. The activated platelets have thepotential to be deposited on the valve or downstream from the valve andto aggregate into thrombi. Furthermore, the activated platelets and thereleased biochemical agents initiate a coagulation cascade. Therefore,valves with mean forward flow velocities and peak shear stresses whichare lower than prior art valves would be beneficial to patients.

SUMMARY OF THE INVENTION

A heart valve prosthesis for implantation in the heart of a patientincludes a valve housing or body providing a lumen therethrough. Atleast one occluder in the lumen coupled to the valve body is movablebetween an open position allowing blood flow through the lumen and aclosed position in which blood flow through the lumen is blocked. Thevalve housing includes a first annulus and a second annulus spaced apartfrom the first annulus. The first and second annuli are on opposite endsof the valve housing. A suture cuff is provided for attaching the valvehousing to heart tissue of a patient.

A cuff retention mechanism is positioned between the first and secondannuli for attaching the suture cuff to the valve housing. The suturecuff and at least the part of the cuff retention mechanism nearer thetissue annulus is spaced apart from the first annulus and the secondannulus, providing tissue impingement barriers therebetween. The absenceof suture cuff and cuff retention mechanism from the impingement barrierat the tissue annulus facilitates efficient lumenal utilization of theavailable tissue annulus area and thereby provides a significantbeneficial feature.

In one embodiment, the cuff retention mechanism includes first andsecond rims which protrude from the valve housing. In anotherembodiment, the retention mechanism includes a single rim protrudingfrom the valve housing. The cuff retention mechanism supplies support tothe valve housing thereby strengthening the valve housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top plan view of a heart valve without a suture cuff inaccordance with the invention.

FIG. 1B is a cross-sectional view of the heart valve shown in FIG. 1A.

FIG. 1C is a cross-sectional view of the heart valve depicted in FIG.1A.

FIG. 2A is a cross-sectional view showing a heart valve in accordancewith the invention implanted in a heart.

FIG. 2B is a cross-sectional view of the heart valve of FIG. 2A rotated90° attached to a heart.

FIG. 3 is a cross-sectional cutaway view of a portion of a heart valvein accordance with another embodiment of the invention.

FIG. 4 is a cross-sectional view of a heart valve in accordance withanother embodiment attached to a heart.

FIG. 5 is a cross-sectional view showing a suture cuff attached to theheart valve depicted in FIG. 1A.

FIG. 6 is a cross-sectional view showing a suture cuff attached to theheart valve depicted in FIG. 4.

FIG. 7 is a cross-sectional view showing a suture cuff attached to aheart valve in accordance with another embodiment.

FIG. 8 is a cross-sectional view showing a suture cuff attached to aheart valve in accordance with another embodiment.

FIG. 9 is a cross-sectional view showing a suture cuff attached to aheart valve in accordance with another embodiment.

FIG. 10 is a cross-sectional view showing a suture cuff attached to aheart valve in accordance with another embodiment.

FIG. 11 is a cross-sectional view of a heart valve prosthesis inaccordance with another embodiment.

FIG. 12 is a cross-sectional view of a heart valve prosthesis inaccordance with another embodiment.

FIGS. 13A, 13B, 14A and 14B are cross-sectional views of heart valveprostheses used to illustrate one aspect of the invention.

FIGS. 15A, 15B and 15C are perspective and side plan views of heartvalve prostheses in accordance with another embodiment.

FIG. 16 is a cross-sectional view of a heart valve prosthesis havingrims in accordance with another embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For implantation of a prosthetic valve in the aortic position, a surgeontypically opens the aorta and excises the native valve. The surgeon theninserts the prosthetic valve through the opening in the aortic wall andsecures the prosthesis at the junction of the aorta and the leftventricle. The inflow annulus of the valve faces the left ventricle and,relative to the surgeon's perspective, may be termed the distal annulus,while the outflow annulus of the valve faces the aorta and may be termedthe proximal annulus.

For implantation of a prosthetic valve in the mitral position, a surgeontypically opens the left atrium and excises the native valve. Thesurgeon then inserts the prosthetic valve through the opening in theatrial wall and secures the prosthesis at the junction of the leftatrium and the left ventricle. The inflow annulus of the valve faces theleft atrium and, relative to the surgeon's perspective, may be termedthe proximal annulus, while the outflow annulus of the valve faces theleft ventricle and may be termed the distal annulus. Thus, the distalportion of the valve may be defined as the portion of the valvetypically seated intra-annularly, for either the aortic or mitralposition.

The invention provides an improved heart valve prosthesis with anincreased valve lumen achieved through a thin intra-annular barrier andplacement of cuff and retention members supra-annularly to the tissueannulus. A cuff retention mechanism is provided between a first inflowannulus and a second outflow annulus of the orifice housing of thevalve. In one embodiment, the cuff retention mechanism includes firstand second rims which protrude from the valve orifice housing, with eachrim spaced apart from its respective nearer annulus, thereby allowingthe valve to be used for either aortic or mitral replacement whilemaintaining all the invention's beneficial features. In a secondembodiment, the retention mechanism is a single rim protruding from thevalve orifice housing and spaced apart from either annulus. In a thirdembodiment with two rims, only one rim is spaced apart from its nearerannulus while the other rim extends along its nearer annulus. Thisembodiment maintains all the beneficial features of the invention onlywhen used either as an aortic replacement, for the case when theupstream rim is spaced from its annulus, or as a mitral replacement, forthe case when the downstream rim is spaced from its annulus. In a fourthembodiment, the cuff retention mechanism includes a metal or polymercuff retaining ring, the inner surface of which includes at least oneradial projection, such as a key or rim, which mates with at least onecircumferential groove or slot on the exterior of an orifice housingwithout rims, and spaced apart from the annuli, so as to preventsignificant motion of the cuff retention mechanism parallel to thecentral or flow axis of the valve after assembly. In a fifth embodiment,the groove or slot lies in a thicker section of the orifice which isspaced apart from an annulus. In a sixth embodiment, a thin section orlip extends intra-annularly from a suture cuff retention ring whichcaptures the valve housing. In at least one embodiment, the cuffretention mechanism provides support and stiffness to the valve housing,thereby helping assure that the occluders are not inadvertently releasedby surgical manipulations. In another embodiment, a rim may beinterrupted or discontinuous or a groove may be formed between the rims.

FIGS. 1A, 1B and 1C are top plan and cross-sectional views,respectively, of heart valve 10 in accordance with the invention withthe suture cuff not illustrated. Valve 10 includes a generallyring-shaped orifice support housing (also referred to as an orifice,orifice ring or orifice body) 12 forming a lumen 17 and having pivotguards 14. Pivot guards 14 include occluder mated spherical pivots 18having opening stop 18 a and closing stop 18 b for occluders or leaflets16. In FIG. 1A, leaflets 16 are shown in an open position while in FIG.12 leaflets 16 are shown in the open position and in the closed positionin phantom.

As shown in FIG. 1B, orifice body 12 includes generally circumferentialbody protrusions (or rims) 20 and 22. Protrusions 20 and 22 are spacedapart from either annulus of the orifice and toward a central plane P oforifice 12 to provide thin projections or lip portions 24 and 26. Lips24 and 26 provide an engagement surface for the tissue annulus of aheart. For aortic and mitral replacement valves, respectively, theperipheries of lips 24 and 26 are tissue impingement barriers. Lips 26and 24 serve as barriers to tissue encroachment into the valve lumenfrom the tissue which grows into the suture cuff. A sewing ring orsuture cuff 50 (shown in FIGS. 2A and 2B) is attached between rims 20and 22.

Generally, in preferred embodiments described herein, the orifice mayconsist of a pyrolytic carbon coating 30 which is deposited onto agraphite substrate 32 by a chemical vapor deposition (CVD) process.

Turning now to FIGS. 2A and 2B, aortic implantation of heart valve 10 inheart 40 is shown in cross section. FIG. 2B is similar to FIG. 2A exceptvalve 10 is rotated 90°. Heart 40 includes aorta 42, left ventricle 44and coronary ostium 46. Valve 10 is shown positioned in heart tissueannulus 48. Valve 10 includes an inflow annulus 27 and an outflowannulus 29. Lip 24 is adapted to receive tissue annulus 48 between rim20 and the inflow annulus 27 of orifice 12 proximate the left ventricle44. FIGS. 2A and 2B also show suture cuff 50 secured between rims 20 and22. Suture cuff 50 is used to suture valve 10 to heart tissue, therebysecuring valve 10 in position as shown in FIGS. 2A and 2B and preventingperivalvular leakage.

As shown in FIGS. 2A and 2B, lips 24 and 26 act as tissue impingementbarriers to prevent ingrowth of heart tissue into orifice 12. Lip 24provides an orifice annulus for engagement or apposition with the tissueannulus 48 of heart 40. The upstream 51 and downstream 53 planes ofsewing cuff 50 are generally located within the confines of rims 20 and22. Cuff 50 and rims 20 and 22 are entirely supra-annular in implantedvalve 10. Lip 24 provides an extension of the orifice 12 into the planeof the tissue annulus 48. The outside diameter of orifice 12 at lip 24generally conforms to the inside diameter of tissue annulus 48.Additionally, a portion of lip 24 is intra-annular with pivot guards 14extending subannularly. The intra-annular projection of lip 24 reducesthe probability of overgrowth of tissue from tissue annulus 48 into thevalve lumen. This is advantageous since such tissue overgrowth tends toreduce the lumen area, disturbs the flow and may encroach on the valvemechanism, reducing the effectiveness of the heart valve. The subannularextension of pivot guards 14 reduces the height of orifice 12 protrudinginto the aortic root thereby reducing the likelihood of blockage ofcoronary ostium 46. Lip 26 may be used to reduce tissue growthprogressing from the cuff 50 onto the outflow annulus 29 and into thevalve lumen 17.

For the mitral position, lip 26 is positioned intra-annularly, and lip24 and pivot guard 14 are positioned supra-annularly. Lip 24 may be usedto reduce the probability of tissue growth progressing from cuff 50 ontothe inflow annulus 27 and into the valve lumen 17.

FIG. 3 shows a cross-sectional view of a portion of a valve 100 inaccordance with a second embodiment. Valve 100 includes orifice housing102, including single protrusion rim 104. Single rim 104 is positionedproximate plane P through the approximate center of orifice 102. Tissueimpingement barrier lips 106 and 108 are formed on either side of rim104 between rim 104 and the ends of orifice 102. A suture cuff 110(shown in FIG. 4) is attached to rim 104.

FIG. 4 is a cross-sectional view of valve 100 implanted in heart 40.Numbering of similar elements in valve 100 is consistent with thoseelements in valve 10. In FIG. 4, valve 100 includes suture cuff 110which is used by a surgeon to suture valve 100 to tissue of heart 40. Asshown in FIG. 4, the seating and engagement of valve 100 in tissueannulus 48 is similar to that of valve 10 shown in FIGS. 2A and 2B. Cuff110 and the majority of orifice 102 is supra-annular. For aorticimplantation, tissue impingement barrier lip 106 is intra-annular whilepivot guards 14 extend subannular.

FIG. 5 is a cross-sectional view of valve 10, as shown in FIGS. 1A, 1B,1C, 2A and 2B, which shows attachment of suture cuff 50 to orifice 12. Ametal, polymer or other biocompatible material attachment ring 120 fitsbetween rims 20 and 22 and pinches or clamps cuff 50. Cuff 50 comprises,for example, a polyester or PTFE knit or a PTFE felt, or other soft,conformable material known in the art. FIG. 5 shows the initiation oftissue ingrowth 122 into cuff 50 from the heart tissue adjacent tissueannulus 48. Assembly of the suture cuff to the orifice may be throughany appropriate technique known in the art. In one embodiment, ring 120is initially in a flattened condition such that the tips of the “U”shape are spread apart. Ring 120 is placed between rims 20 and 22 usinga relatively uniform expansion technique in which ring 120 is slid overa conical mandril (not shown) and over one of the two rims 20, 22 untilit is positioned as shown in FIG. 5. Ring 120 is a stiffener for theorifice and can be used to attach the cuff in a rotatable manner Cuff 50is placed around the outer circumference of ring 120 and the sides ofring 120 are bent as shown in FIG. 5. Friction between cuff 50 and ring120 maintains cuff 50 in position. Additionally, sutures, staples, pins,adhesives or other such device or material may be used to adhere cuff 50to ring 120 or directly to orifice 12.

FIG. 6 is a cross-sectional view of a portion of valve 100 shown inFIGS. 3 and 4, providing a detailed view showing attachment of suturecuff 110 to orifice 102 at rim 104. A metal, polymer or otherbiocompatible material attachment ring 130 is attached to cuff 110 andcrimped around and onto rim 104. Prior to attachment, ring 130 liesrelatively flat. Scoring 132 is provided on ring 130 to promote bendingof ring 130 at the desired locations. Ring 130 is crimped by applyingpressure to opposing sides of ring 130 such that ring 130 bends atscoring points 132.

FIG. 7 is a cross-sectional view showing orifice 12 having rim 220forming tissue impingement barriers 224 and 226. Rim 220 includes groove230 formed therein. A mating key or rim 240 of cuff retaining ring 250engages mating groove 230 of orifice 12. Rim 220 of orifice 12 is ofsufficient thickness to form groove 230 therein without deleteriouslydecreasing the strength of orifice 12. Cuff 260 is captured in ring 250.

FIG. 8 is a cross-sectional view of orifice 12 having a cuff retentionmechanism in accordance with another embodiment in which a projectionfrom the cuff retention mechanism ring itself forms a tissue impingementbarrier and inflow or outflow annuli. Cuff 350 is retained between rims340 and 345 of ring 360. Tissue impingement barriers 324 and 326 areformed between extensions of ring 360. Ring 360 comprises abiocompatible metal such as titanium or cobalt-chrome alloy and extendspast the valve housing so as to serve as the tissue impingement barrier.Cuff 350 may be retained by suture 355 wrapped around the annulus formedbetween rims 340 and 345. Radially inward extensions 313 capture orifice12.

FIG. 9 is a cross-sectional view of orifice 102 attached to cuff 150 inaccordance with another embodiment. A spring clip ring 152 extendsaround the outer circumference of orifice 102 and grasps rim 104.Preferably, cuff 150 is formed around spring clip ring 152. The cuffclip assembly is snapped onto valve rim 104. Alternatively, ring 152includes tips 154 which clamp the fabric of suture cuff 150.

FIG. 10 is a cross-sectional view of orifice 102 attached to suture cuff160 in accordance with another embodiment. Attachment mechanism 162includes disks 164 which extend around the outer circumference oforifice 102. Disks 164 are connected together by band 166 which providesa friction fit with rim 104 of orifice 102. Sewing cuff 160 is securedto band 166 between disks 164 by suture windings 168. In alternativeembodiments, disks 164 and band 166 can be formed integrally as a singlepiece or separately and attached together. This may be through the useof a biocompatible adhesive, or similar material, or a friction fitbetween protrusions from band 166 and openings in disks 164.

In prior art, the stiffness of the orifice has typically been increasedby increasing the area of the orifice wall section, which for a giventissue annulus diameter reduces the area of the lumen. One aspect ofthis invention includes providing the orifice stiffness for a giventissue annulus diameter without reducing lumen area. In one or moreembodiments of the current invention the stiffness of the orifice isenhanced by rims projecting from the orifice. It has been discovered anddemonstrated that the size, shape and placement of the rims enhance thestiffness.

FIG. 11 shows a cross-sectional view of a heart valve prosthesis orifice480 in the aortic position in accordance with another embodiment whichincludes housing 482 and pivot guard 484 which carries a pivot 486.Housing 482 is formed on substrate 485. Rims 488 and 490 extend aroundthe outer circumference of housing 482 and form outflow proximal implantlip 492 and inflow distal lip 494. A middle surface 496 is formedbetween rims 488 and 490. A suture cuff 498 fits between rims 488 and490 around middle surface 496 and is used to attach heart valve orifice480 to heart tissue annulus 500. The size of orifice 480 is selectedsuch that tissue annulus 500 substantially conforms to the diameter ofdistal lip 494. However, the majority of orifice 480 and suture cuff 498are positioned supra-annular relative to tissue annulus 500.

Rims 488 and 490 have a radial height h which is greater than that oftypical prior art designs. In a preferred embodiment, h is greater thanabout 0.25 mm and is preferably about 1 mm. It has been discovered thatby increasing the dimension h, additional stiffness is provided tohousing 482. Additionally, the increase in the h dimension of rims 488and 490 protects the cuff retention mechanism 499 of suture cuff 498. Inone embodiment, retention mechanism 499 comprises sutures. However, anymechanism may be used such as a polymer or metal band or a ring. In oneor more embodiments, retention mechanism 499 allows rotation of valvehousing 482 relative to cuff 498 during the implantation procedure. Theadditional protection provided by rims 488 and 490 to the retentionmechanism 499 helps reduce application of excessive pressures tomechanism 499 such as pressure from tissue annulus 500. Such excessivepressures tend to change the amount of torque required to rotate housing482 relative to cuff 498. Furthermore, the increased height h of rims488, 490 further reduce the likelihood of tissue ingrowth from tissueannulus 500 into the lumen 497 of orifice 480. Further still, theincreased height h of rims 488,490 increases the ability to retain thesuture cuff 498 between rims 488, 490.

FIG. 12 is a cross-sectional view of another embodiment of heart valveprosthesis orifice 510 adapted for aortic implantation having housing512. Housing 512 includes pivot guard 514 and pivot 516 formed therein.Distal rim 518 and proximal rim 520 extend around the outercircumference of housing 512 and form middle section 522 therebetween.Rims 518 and 520 are positioned toward the proximal side of prosthesis510 and rim 518 forms distal lip 524 around the outer circumference ofhousing 512. It has been discovered that the offset configuration ofrims 518 and 520 relative to housing 512 provides additional stiffnessfor a given lumen. This allows the interior lumen of housing 512 to beincreased for a given stiffness. Therefore, the lumen area is increasedwhile providing orifice stiffness. Furthermore, the configuration shownin FIG. 12 allows for greater length 1 of distal lip 524 which providesfor deeper sub-annular placement and a larger intra-annular impingementbarrier. It also decreases the valve supra-annular profile to reduce thepotential for blockage of the coronary ostia. The design shown in FIG.12 also includes an increased rim height h as described above for theembodiment of FIG. 11.

FIGS. 13A and 13B show orifices 610 and 510, respectively. Orifice 610is an embodiment adapted for implant in the mitral position, with pivotguards 620 supra-annular (in the left atrium) and orifice 510 is anembodiment adapted for implant in the aortic position, with pivot guards520 subannular (in the left ventricular outflow tract). Orifice 610 isshown acted upon by hypothetical force F generated by the mitral valvetissue annulus. Orifice 510 is shown acted upon by hypothetical force Ggenerated by tissues within the left ventricular outflow tract below theaortic annulus. FIGS. 14A and 14B are cross-sectional views of heartvalve prostheses 480 and 510, respectively. FIGS. 13A, 13B, 14A and 14Bare provided to illustrate the relationship between the placement of therims and the stiffness of the prosthesis orifice. A comparison of thestiffness of valves 510 and 480 follows.

The stiffness, or ability of the housing to resist loading, is dependenton the orifice geometry and material elastic modulus. The presentinvention provides a technique for increasing stiffness for a givenmaterial. The method increases resistance to both translational andtorsional loads on the orifice and to combinations thereof. Thegeometric parameter that is used to analyze and determine stiffness isthe area moment of inertia which, for a given material, is directlyproportional to stiffness. There are three area moments of inertiaassociated with an area, Ix, Iy and Jo (polar moment of inertia). The Imoments are each associated with an axis in the plane of the area, suchas x and y in FIGS. 14A and 14B, and the polar moment of inertia Jo isassociated with rotation, and therefore, an axis perpendicular to theplane.

The polar moment of inertia of the area is the simple algebraic sum:

Jo=Ix+Iy  Eq. 1

Thus, if either Ix or Iy is increased, the ability of the structure toresist rotation is increased. Other important rules of area moments ofinertia are:

The Additive rule:

For the orifice body, Ix=Ix₁+Ix₂+Ix₃ where Ix_(i) is the moment ofinertia of area i (where i=1,2,3) with respect to the x axis of theentire system.

The Parallel axis theorem:

I_(xi)=I_(xilocal)+A_(i)D_(i) ² where I_(xilocal) is the moment ofinertia of area i with respect to its centroid and A_(i)D_(i) ² is thetransformation for the offset in the area's axis with respect to thesystem's axis. Quantity D_(i) is the distance from the local area's xaxis and the system's x axis and A_(i) is the area of the local element.Furthermore, for a rectangle I_(local)=(Width×Height³)/12. Height andWidth are relative to the axis of the moment, i.e., the width for Iy isthe height for Ix. Equations of the same form are also true for Iy.

The difference between the orifice 480 and 510 is the distance “ν” shownin FIGS. 14A and 14B, respectively. For the purpose of this explanation,all lettered dimensions are the same in orifice 480, 510, and orifices480, 510 are made from the same material. This implies that the local Imoments are equal for both designs since the heights and widths of theareas do not change. The only portion of the I moments that change isthe parallel axis portion AD², specifically the D. It can be seen thatthe Dy of the system remains unchanged as dimension ν is changed.Therefore, the Iy's are equal for both designs. The parallel axisportions (D_(i) ²) of Ix changes as area A₃ is shifted downward. Oneaspect of the invention for one or more embodiments moves structure awayfrom the neutral axis. The change is described mathematically asfollows:

Parallel axis theorem portion:

For the embodiment of FIG. 14A, valve 480, a prime sign ′ will be used.Due to symmetry about the x axis, D′₁=0, D′₂=(z+H₂)/2, and D′₃=−(z+H₂)/2For valve 480 shown in FIG. 14A: $\begin{matrix}\begin{matrix}{{I\quad x^{\prime}} = \quad {{\sum I_{xilocal}^{\prime}} + {A_{1}D_{1}^{\prime \quad 2}} + {A_{2}D_{2}^{\prime \quad 2}} + {A_{3}D_{3}^{\prime \quad 2}}}} \\{= \quad {{\sum I_{xilocal}^{\prime}} + {A_{2}\left( {\left( {z + H_{2}} \right)/2} \right)}^{2} + {A_{3}\left( {{- \left( {z + H_{2}} \right)}/2} \right)}^{2}}}\end{matrix} & {{Eq}.\quad 2}\end{matrix}$

For Ix of valve 510 shown in FIG. 14B: The neutral axis of the valve 510is shifted downward and is assumed to be at the midpoint between therims. The difference in stiffness is defined below. For any givenmaterial the difference in stiffness is proportional to the differencesin area moments of inertia.

Area stiffness is proportional to I_(x)−I_(x)′. Therefore, ifI_(x)>I_(x)′, then the design is stiffer.

Given:

I′_(xilocal)=I^(ε) _(xilocal)  Eq. 3

Therefore:

I_(x)−I′_(x)=A₁D₁ ²+A₂D₂ ²+A₃D₃ ²−[A₁D′₁ ²+A₂D′₂ ²+A₃D′₃ ²]  Eq. 4

Since area A₃ is shifted downward the centroid will also be shifteddownward thus causing D₁≈0. Therefore;

A₁D₁ ²>AD′₁ ²=0  Eq. 5

$\begin{matrix}{D_{2}^{\prime \quad 2} = {D_{3}^{\prime \quad 2} = \left( \frac{z + H_{3}}{2} \right)^{2}}} & {{Eq}.\quad 6} \\{D_{2}^{2} \approx D_{3}^{2} \approx \left( \frac{z + v + H_{3}}{2} \right)^{2}} & {{Eq}.\quad 7}\end{matrix}$

Therefore:

A₂D₂ ²>A₂D′₂ ² and A₃D₃ ²>A₃D′₃ ²  Eq. 8

From this it can be seen that:

I_(x)−I′_(x)=[A₁D₁ ²−A₁D′₁ ²]+[A₂D₂ ²−A₂D′₂ ²]+[A₃D₃ ²−A₃D′₃ ²]>0  Eq. 9

The difference is positive therefore the area moment of inertia andstiffness are greater for the aortic or mitral specific design. Theanalytic derivation of the centroids and offsets have not been shown.However, one skilled in the art could derive these equations.

FIG. 15A is a perspective view and FIGS. 15B and 15C are side plan viewsof a heart valve orifice 540 in an aortic position in accordance withanother embodiment. Orifice 540 includes housing 542, pivot guards 544,distal rim 546 and proximal rim 548. Proximal rim 548 is positionedsimilar to proximal rim 520 shown in the embodiment of orifice 510.However, distal rim 546 has two segments, 546A and 546B. FIGS. 15B and15C show a retention ring 550 which may be used to attach, for example,a suture cuff to orifice 540. It has been discovered that it isdesirable in some instances for ring 550 to be a continuous member.However, if ring 550 is continuous it must be stretched over a rim of atypical prior art prosthesis. Such a stretchable ring may perform poorlyin retaining the cuff to the orifice. In contrast, ring 550 is acontinuous stiff ring and is placed over rim 546 by placing ring 550 atan angle to the axis of prosthesis 540 as shown in FIG. 15B. As shown inFIG. 15B, first one side of ring 550 is slipped over segment 546B of rim546 and then the other side of ring 550 is slipped over segment 546A asshown in FIG. 15B.

In the embodiment of prosthesis 540, proximal rim 548 is offset similarto FIG. 12 to provide the increased stiffness as discussed above.Furthermore, segments 546A and 546B are positioned between pivot guards544 to increase the stiffness in the relatively compliant portion ofhousing 542. Specifically, pivot guards 544 provide stiffness to housing542 and segments 546A and 546B are positioned between pivot guards 544to provide additional stiffness in this region of housing 542.Furthermore, the proximal rim 548 of orifice 540 can resist the load ofthe aortic blood pressure applied to the closed valve. Proximal rim 548provides additional stiffness to the proximal side of orifice 540 toaccommodate these loads during implantation. Distal lip 554 has anenlarged length 1 (see FIG. 15C) to provide a better interface with theheart tissue annulus, similar to that discussed with respect to FIG. 12.

FIG. 16 is a cross-sectional view of a heart valve prosthesis 560 in anaortic position in accordance with another embodiment which includeshousing 562 and pivot guard 564. Proximal rim 566 and distal rim 568extend around the circumference of housing 562 and form a V-shapedgroove 570 therebetween. Rims 566 and 568 are offset in a proximaldirection with respect to the surgeon in a typical surgical approach toprovide distal lip 572. Rims 566 and 568 extend over a relatively largearea of the outer circumference of housing 562 and provide a slope togroove 570 which carries retention mechanism 574. This is in contrastwith a typical rim in which there is a step thickness differential suchas in FIG. 1B. Retention mechanism 574 may be any appropriate element tocouple a suture cuff to groove 570 such as a V-shaped compliant orexpandable ring, such as a spring ring.

One aspect of the invention provides an increase in the effectiveorifice area of the orifice relative to the available tissue annulus 48area of heart 40. As discussed above, a small prosthetic valve lumen inthe aortic position results in high systolic transvalvular pressuregradients which excessively burden the left ventricle. Furthermore, asmall lumen has been related to thrombus and thromboembolism formation.Factors relating to increased risk of thrombus and thromboembolisminclude the non-physiological surfaces and blood flows introduced bymechanical valves. Additionally, a small lumen results in increasedshear stress due to higher mean velocity in the blood flow. An increasein lumen area as set forth herein provides reduced transvalvularpressure gradients and reduced mean velocity and thereby reduced shearstress, and therefore a reduction in the potential formation of thrombusand thromboembolism. This is achieved by providing a valve orifice 12with an inner lumen diameter (d₂ in FIG. 1A) of a generally cylindricalinterior bounded by two generally planar segments proximate pivot guards14 which are generally perpendicular to the axis of rotation of leaflets16. In one embodiment, the distance d₁ between the lumenal planes ofpivot guards 14 is not less than about 85% of diameter d₂ shown in FIG.1A. Diameter d₂ is not less than about 85% of tissue annulus diameterd₃. Diameter d₃ is the diameter to the outer edge of orifice 12 but doesnot include the outer diameter of rims 20 or 22. These dimensionalrelationship provide increased lumen area. However, as the relativethickness of the heart valve orifice 12 is reduced, the stiffness ofvalve orifice 12 decreases. One aspect of the invention includesstiffening the orifice with rims as shown in FIGS. 1, 3, 5, 6, 7, 8, 9,10, 11, 12, 13, 15 and 16. It is within the contemplation of thisinvention to use a plurality of such rims or protrusions. The additionalstiffness provided by at least one rim supplements any reduction inorifice housing stiffness which otherwise could occur due to the thinsection.

Rings 120, 130, 152, 162, 250, 360, 550, 574 shown in FIGS. 5, 6, 7, 8,9, 10, 15 and 16 provide additional stiffness which also allowsincreased lumen area. The rings 120, 130, 152, 162, 250, 360, 550, 574may be channeled beam shapes, such as I, V, U or H configurations, whichare known in the art to provide additional stiffness. Rings 120, 130,152, 162, 360, 550, 574 extend the width of the suture cuff to provideeasier stitching during implantation and help to prevent perivalvularleakage. Another advantage of the retention rings described herein isthat they are easily assembled with a heart valve. The attachment ringsare well suited for an orifice having a reduced thickness and made ofrelatively low elastic modulus materials such as CVD pyrolytic carbon.Rings 120, 130, 152, 162, 550, 574 are adapted for mechanization orautomation of the assembly process. Furthermore, rings 120, 130, 152,162, 550, 574 allow the suture cuff to rotate relative to the orifice.Cuff rotation torque may be controlled by controlling friction betweenthe cuff attachment ring and the orifice body. Friction can becontrolled by adjusting the crimping force of rings 120, 130, 152, 162.

The valves set forth herein may be fabricated with any appropriatebiocompatible material. In preferred embodiments, the orifice may be ofa pyrolytic carbon-coated graphite or other material which isthromboresistant, durable and of sufficient strength, stiffness andfracture resistance. The orifice may consist of a durable, bloodcompatible coating or film on a substrate. In one embodiment, thecoating or film is diamond-like carbon, and the substrate is a metal.Suitable metal substrates include, but are not limited to, titanium andits alloys.

The present invention provides a mechanical heart valve for a smallaortic root which significantly reduces stenosis while maintaining anintra-annular barrier which blocks tissue overgrowth of the valvingmechanism and lumen. The invention is applicable and beneficial for anysize aortic root and to the mitral position. When implanted in theaortic position, the invention beneficially decreases the work load ofthe left ventricle. Anticipated patient benefits are increased toleranceto exercise, increased rate of regression of left ventricularhypertrophy, and lower incident rate of congestive heart failure. Theembodiments set forth herein provide better hemodynamics by means of arelatively low blood flow mean velocity, thus reducing shear stress andthereby reducing the potential for thrombosis. The relatively low meanvelocity is attained by increasing the area of the valve lumen. Low meanvelocity also provides a decreased occluder drag, since drag isproportional to the square of velocity, thereby further contributing toan increased effective orifice area. Circumferential protrusions or rimsare used for attaching the heart valve housing to a suture cuff. Cuffretention mechanisms set forth herein, including rims or protrusions,and attachment rings, are provided which increase the stiffness of thevalve body and which provide rotatable coupling. The protrusions providestiffness to the valve housing thereby allowing the intra-annular andsub-annular thicknesses of the valve housing to be reduced in order toincrease the lumen diameter. The supra-annular portion of the valve isof sufficient thickness to provide strength and stiffness. The variousembodiments set forth herein provide increased stiffness by selectiveplacement of the rims; provide increased rim height for improved cuffretention; provide increased rim height to protect the cuff attachmentand/or rotation mechanisms placed between the rims; provide a largertissue impingement barrier; reduced supra-annular height to reduce thelikelihood of interference with the coronary ostia.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. For example, although this description hasbeen largely directed to an aortic mechanical valve, the techniques arealso applicable to mitral mechanical heart valves.

What is claimed is:
 1. A heart valve prosthesis for replacing a nativevalve in a tissue annulus of a heart of a patient, comprising: amonolithic single piece valve orifice housing providing a lumentherethrough and having an outer circumference, a distal annulus, pivotguards, and upstream and downstream rims integral with the rest of thehousing and which define a middle surface therebetween and formed on themonolithic single piece housing, the rims having rim diameters andextending around the outer circumference of the housing adapted toprovide additional stiffness to the single piece valve orifice housing,the pivot guards positioned to provide stiffness to the valve orifice;at least one occluder coupled to the orifice housing movable about apivot axis between an open position and a closed position in which flowthrough the lumen is substantially blocked, wherein the pivot axis isconfigured to be positioned on an upstream side of the tissue annulus ofthe heart and on the pivot guards of the orifice housing; a flexiblesuture cuff configured to couple to the orifice housing between the rimsaround the middle surface and to a proximal side of the tissue annulusof the heart by a cuff retention mechanism; and a lip formed with thesingle piece valve housing and defined in the outer circumference of thehousing between and the distal annulus and having a diameter less thanthe rim diameter, the lip configured to extend through the tissueannulus and generally conforming to the tissue annulus whereby the rimsand suture cuff do not substantially limit the area of the lumen of thehousing.
 2. The prosthesis of claim 1 wherein the suture cuff isrotatably coupled to the valve housing.
 3. The prosthesis of claim 1wherein a diameter of the lumen is greater than about 85% of a diameterof the lip.
 4. The prosthesis of claim 1 wherein the valve prosthesis isadapted for aortic valve replacement.
 5. The prosthesis of claim 1wherein the valve prosthesis is adapted for mitral valve replacement. 6.The prosthesis of claim 1 including a second lip whereby the prosthesisis adapted for both mitral and aortic valve replacement.
 7. Theprosthesis of claim 1 wherein the orifice housing is fabricated frompyrolytic carbon or an alloy of pyrolytic carbon.
 8. The prosthesis ofclaim 1 wherein the valve orifice housing includes a coating or film ofa durable and blood compatible material.
 9. The prosthesis of claim 1further comprising: a circumferential ring generally conforming to thevalve orifice housing and between the rims, the ring adapted forclamping onto the suture cuff thereby securing the suture cuff to thevalve orifice housing.
 10. The prosthesis of claim 1, wherein the cuffretention mechanism comprises: a ring coupled to the rims and to thesuture cuff thereby securing the suture cuff between the rims.
 11. Theprosthesis of claim 10, wherein the ring comprises a spring clip. 12.The prosthesis of claim 10, wherein the ring clamps onto the suturecuff.
 13. The prosthesis of claim 1 wherein the rims have a height h ina radial direction to provide stiffness to the housing.
 14. Theprosthesis of claim 13 wherein the cuff retention mechanism includesmeans for attaching the suture cuff to the orifice housing positionedbetween the rims and wherein an outer diameter of the means forattaching is less than outer diameters of the rims.
 15. The prosthesisof claim 1 wherein one of the rims is segmented into at least two rimsegments to facilitate placement of the suture cuff between the rims.16. The prosthesis of claim 15 including a continuous ring in the suturecuff to maintain attachment of the suture cuff to the housing.
 17. Theprosthesis of claim 1 further including a V-shaped groove definedbetween the rims.